1. Field of the Invention
The invention relates in general to a close loop control system and method of the same, and more particularly to a close loop control system, which uses two detecting units to generate two feedback signals and accordingly determines if the feedback signals are regular, and method of the same.
2. Description of the Related Art
The close loop control system is an essential structure of a variety of automatic control systems, such as water pressure control of the cold water, warm water, and hot water supply systems, the temperature, humidity and static pressure control of the clean room, the static pressure control of the exhausting system, and the acidity, alkalinity or conductivity control of the air conditioning system. The close loop control system uses the detecting unit to feed back signals relative to the control variable for reference of the control unit in program calculating, comparing, and output correction in order that the control variable can be stabilized to the predetermined target value.
Referring to FIG. 1, a block diagram of a conventional close loop control system is shown. The close loop control system 100 includes a controlled system 110, such as a hot water supply system, a detecting unit 120, and a control unit 130. The controlled system 110 has a controlled variable, such as the rotating velocity of the pump motor in the hot water supply system. The detecting unit 120 is a feedback device for detecting the controlled system 110 and outputting a feedback signal A, such as the water pressure, relative to the control variable. The control unit 130 performs a proportional integrated differential (PID) operation, in which the controlled variable of the controlled system 110 is adjusted so that the control variable can reach the expected value according to the comparison between the feedback signal A and a predetermined target value Ao.
When the feedback signal A is larger than the target value Ao, it means that the water pressure (the control variable) supplied by the hot water supply system (the controlled system 110) is too high. Accordingly, the control unit 130 lowers the rotating velocity of the pump motor (the controlled variable) in order to reduce the water pressure. When the feedback signal A is smaller than the target value Ao, it means that the water pressure supplied by the hot water supply system is too low. Accordingly, the control unit 130 increases the rotating velocity of the pump motor to heighten the water pressure.
However, due to the lifetime, quality, and exterior damage issues of the detecting unit 120, its sensing device will be broken down, its pressure guiding tube or connectors will be leaking, and even its transmission device, wires and input module would be irregular. For this reason, the feedback signal A output by the detecting unit 120 will be irregular and thus cannot reflect the real state of the controlled system 110. For example, the present rotating velocity of the pump motor is 1100 rps, and the corresponding water pressure is 20.5 kg/cm2, while the predetermined target value Ao is 20 kg/cm2, and the corresponding rotating velocity of the pump motor is 1050 rps. For the feedback signal A is irregular, the feedback signal A received by the control unit 130 will be fixed to 19 kg/cm2. Therefore, the control unit 130 will determine that the motor rotates too slowly and then increase the rotating velocity until the motor is out of control and the whole hot water supply system is damaged.
Ordinarily, the close loop control system cannot determine if the feedback signal is irregular. Therefore, the above-mentioned system out-of-control issue will occur easily which influences the production and increases the risk of system damage. In addition, when the system sends out the error alarm, mechanics should go to the work field, stop and repair the system by hand, and restart the system after the repair. The system cannot operate continuously as the feedback signal is irregular, thereby influencing the subsequent controlling procedures.